Transmission was 25 times as intensive among classmates as between children in different grades. And yet sitting next to a student who was infected did not increase the chances of catching flu.

Social networks were apparently a more significant means of transmission than seating arrangements. Students were four times as likely to play with children of the same sex as with those of the opposite sex, and following this pattern, boys were more likely to catch the flu from other boys, and girls from other girls.

The scientists found no difference in transmission rates during the closure versus the rest of the outbreak – confirming earlier studies that show how schools need to be closed early in an epidemic to have any effect on transmission.

“This information could be used to understand whether it might be better to close a school, or to close individual classes or grades,” Cauchemez says. These findings were published in Proceedings of the National Academy of Science.

Across the pond, in another swine flu study that came out last week, researchers found that while widespread, sustained school closures are costly and disruptive, they do help hospitals out.

These researchers created a mathematical model to assess how much school closures actually reduce the strain on hospitals.

The team, led by Thomas House of the University of Warwick, input many factors from the 2009 pandemic in England into their model: from available adult bed space to staff shortages at clinics and hospitals if healthcare workers have to look after their kids.

They conclude that if an outbreak is serious enough to require measures like school closures, short and localized ones can’t prevent hospitals from exceeding their capacity.

When facing the threat of a severe pandemic, a coordinated and extended period of school closures – though costly – may be necessary to prevent overly packed intensive care units.

Realistically, they say, there is no difference in the strain put on ICUs until at least 50% of schools are closed.